Water Quantity and Dry-Stack Tailings Storage

  • Rosemont’s level of water consumption will be one of the lowest in the world per pound of copper produced.
  • One important way that we will reduce water usage at Rosemont is through the use of dry-stack tailings storage, a leading-edge tailings management technology.
  • The dry-stack, or filtered, method of tailings storage uses 50% to 60% less water than similarly sized mines, has a smaller footprint, is more stable, poses no threat of groundwater seepage or tailings dam failure, and allows for easier land reclamation and rehabilitation.
  • Tailings are the fine mud or silt material that remains after minerals are extracted from ore. Typically, tailings are stored in large, carefully managed tailings ponds, but Rosemont will remove water from its tailings and stack them on dry land in what will be the largest dry-stack tailings facility in North America. Rosemont won’t use tailings ponds filled with water.
  • In addition, with the dry-stack method, about 85% of the water is mechanically filtered from the tailings and reclaimed and reused for mining purposes, reducing the need to draw on local water resources.

Water Replenishment – Replacing What We Use

  • To be a good neighbour – and an innovative project – Rosemont has committed to replacing all of the water used in its operations. This will be achieved by returning water to the local aquifer via recharge of the Central Arizona Project (CAP), a project designed to replenish water in Arizona’s Green Valley Sahuarita area. Rosemont has already purchased and stored 45,000 acre-feet of CAP water in the Tucson Active Management Area Avra Valley and Lower Santa Cruz storage facilities, enough for the first eight years of operations. As part of this initiative, Rosemont expects to provide $28 million to support a project led by the Community Water Company of Green Valley to build an eight-mile pipeline and water-recharge facility that will bring CAP water to the region. To learn more, click here.
  • Rosemont will be a zero-discharge site, meaning all water used in processing will remain on site and be recycled and reused.
  • Rosemont has set up programs to protect residential wells for those living within the vicinity of the project and to protect wells within the project site itself. The program covers pumping equipment repair and replacement and well deepening for the duration of the project.
  • Rosemont will also carefully evaluate and manage stormwater and run-off water from the operation to minimize potential adverse impacts.

Water Quality

Managing and monitoring water quality at the Rosemont Copper Project.
  • Rosemont’s Aquifer Protection Permit requires the operation to monitor groundwater quality and comply with contingency actions should a permitting standard or alert level be triggered. To comply with these requirements, point of compliance wells will be installed around the project to monitor groundwater quality.
  • Rosemont will use best available demonstrated control technologies to minimize impact to groundwater and ensure existing water quality is maintained. These technologies include double-lined process-solution ponds with leak detection and recovery systems. The use of dry-stack tailings technology is also considered best available demonstrated control technologies, as it minimizes seepage from the facility and potential impacts to groundwater.
  • As part of its permitting requirements, Rosemont will conduct on-site and off-site monitoring to evaluate potential impacts of the project on down-gradient water quality.
  • In addition to permit requirements set by state authorities, the US Forest Service has set its own monitoring requirements to ensure water quality at Rosemont. These include: 
    • Monitoring of additional wells beyond the well monitoring sites required by state regulators as well as additional geochemical testing of waste rock, tailings and process water.
    • Waste-rock seepage monitoring using sampling devices installed inside the waste rock.
    • Monitoring of seeps and springs around the site for water quality and flow.
    • Monitoring of surface-water quality and groundwater levels and quality in locations down-gradient of the project site.
    • Monitoring of livestock tank water quality.
    • Periodic modeling of groundwater levels and pit-lake water quality based on updated monitoring and site-sampling data.